Pop-up ad

Pop-up ads or pop-ups are often forms of online advertising on the World Wide Web intended to attract web traffic or capture email addresses. Pop-ups are generally new web browser windows to display advertisements. The pop-up window containing an advertisement is usually generated by JavaScript using cross-site scripting (XSS), sometimes with a secondary payload using Adobe Flash, but can also be generated by other vulnerabilities/security holes in browser security.

A variation on the pop-up window is the pop-under advertisement, which opens a new browser window hidden under the active window. Pop-unders do not interrupt the user immediately and are not seen until the covering window is closed, making it more difficult to determine which web site opened them.

Pop-up ads originated on the Tripod.com webpage hosting site in the late 1990s. Ethan Zuckerman claims he wrote the code to launch advertisements in separate windows as a response to complaints of displaced banner ads. He didn't invent the pop-up window. Zuckerman later apologized for the unforeseen nuisance pop-up ads had evolved into.

Opera was the first major browser to incorporate tools to block pop-up ads; the Mozilla browser later improved on this by blocking only pop-ups generated as the page loads. In the early 2000s, all major web browsers except Internet Explorer allowed the user to block unwanted pop-ups almost completely. In 2004, Microsoft released Windows XP SP2, which added pop-up blocking to Internet Explorer.

Most modern browsers come with pop-up blocking tools; third-party tools tend to include other features such as ad filtering.

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Wikipedia